Personally, I believe that an American comic is not manga, but I prefer to call things like NHS either Foreign-manga, Amerimanga, or (the catch-all) "Manga-inspired." That's what I would call an American comic drawn in the manga style.

1998, "Gwydion", What is the "Manga Style"? (discussion on Internet newsgroup rec.arts.comics.misc)

Every time the subject's come up, I've seen the complaint that "S/he's just copying the manga look, not the layout/storytelling/themes" bandied about over just about any Amerimanga artist you'd care to name. However, I'e [sic] never really seen anyone describe exactly what they *meant* by that. Obviously, they mean more than (as Warren says) "huge eyes and speed-lines". So what else then?